Low melting point disubstituted-p,p&#39;-phenyl cinnamate liquid crystals

ABSTRACT

where R1 and R2 can be n-alkyl (CH3(CH2)n); n-alkoxy (CH3(CH2)nO) and acyloxy (CH3(CH2)nCO2) groups.   A new nematic liquid crystal system is disclosed. The system utilizes disubstituted-p, p&#39;&#39;-phenyl cinnamates as liquid crystals and combines various of these liquid crystals to expand the nematic temperature range of the composite over that of the individual components, thus providing a family of low melting point nematic liquid crystals. These crystals have the general formula

llnited States Patent 1 Jones, Jr. et a1.

[ 51 Dec. 16, 1975 LOW MELTING POINT DISUBSTITUTED-P,P-PIIENYL CINNAMATE LIQUID CRYSTALS [75] Inventors: Freeman B. Jones, Jr., Westlake Village; Joseph J. Ratto, Thousand Oaks, both of Calif.

[73] Assignee: Rockwell International Corporation, El Segundo, Calif.

[22] Filed: Oct. 1, 1973 [21] Appl. No.: 402,531

[52] US. Cl 252/299; 252/408; 260/473 R; 260/476 R; 350/160 LC; 428/1 [51] Int. Cl. C09K 3/34; C07C 69/76 [58] Field of Search 252/299, 408; 350/160 LC; 260/473 R, 476 R; 428/1 [56] References Cited UNITED STATES PATENTS 3,322,485 5/1967 Williams 252/299 3,773,747 11/1973 Steinstrasser 252/408 FOREIGN PATENTS OR APPLICATIONS 2,024,269 12/1971 Germany 252/299 of Liquid Crystal, V. A. UsolTseva et al., Russ. Chem. Rev., Vol. 32, No. 9, pp. 495-507 (1963).

Primary ExaminerLe1and A. Sebastian Assistant Examiner-T. S. Gron Attorney, Agent, or Firm-H. Fredrick I-Iamann; G. Donald Weber, Jr.; Robert Ochis [57] ABSTRACT A new nematic liquid crystal system is disclosed. The system utilizes disubstituted-p, p'-phenyl cinnamates as liquid crystals and combines various of these liquid crystals to expand the nematic temperature range of the composite over that of the individual components, thus providing a family of low melting point nematic liquid crystals. These crystals have the general formula where R and R can be n-alkyl [CH (CH nalkoxy [CH (CH ),,O] and acyloxy [CH (CH ),,CO groups.

10 Claims, No Drawings LOW MELTING POINT DISUBSTITUTED-P,P'-PHENYL CINNAMATE LIQUID CRYSTALS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of liquid crystals and more particularly to the field of nematic liquid crystals.

2. Prior Art Many nematic liquid crystals are known and are used in display applications for electronic readouts. Most of the liquid crystals used in these systems are Schiff-base materials and are liquid crystals at room temperature. The Schiff-base materials unfortunately are highly unstable in the presence of water and ultraviolet light. This requires extreme care in the handling of these materials to prevent contamination and degradation. An example of such prior art liquid crystals is given in US. patent application Ser. No. 297,172, filed Oct. 12, 1972 as a continuation of Ser. No. 86,515, filed Nov. 6, 1970 (now abandoned) by Chang et al, for Nematic Liquid Crystal Compositions which discusses the use of a eutectic mixture of interalia methoxy-benzylidenebutylaniline and ethoxy-benzylidene-butylaniline. Some ways of improving the characteristics of such liquid crystals are disclosed in US. patent applications Ser. Nos. 357,565; 357,566 and 357,567 for Nematic Liquid Crystals Doped to Raise Their Dynamic Scattering Cutoff Frequency; Doping of Nematic Liquid Crystals and Homotropic Alignment of Liquid Crystals in a Display Cell by Baked on Ionic Surfactants, respectively, assigned to the common assignee.

SUMMARY OF THE INVENTION The invention relates to liquid crystal materials and systems. In particular, there is disclosed a disubstitutedp, p'-phenyl cinnamate liquid crystal system. Liquid crystal materials of this class are more stable in the presence of atmospheric contaminants than the prior art Schiff-base materials are. Although individual members of the system have a relatively narrow nematic temperature range, binary and ternary mixtures of properly selected and proportioned members of this liquid crystal system yield liquid crystals having Wide nematic temperature ranges.

Liquid crystals in this system have the following general formula as where R and R can be n-alkyl [CH (CH nalkoxy [CH (CH ),,O] and acyloxy [CH (CH ),.CO groups.

Mixtures of the various liquid crystals within the system are formed by heating the desired proportions of the various components to above their nematic-isotropic transition temperatures to form a solution. The

DESCRIPTION OF THE PREFERRED EMBODIMENT The inventive liquid crystal system comprises cinnamic acid esters having the general formula where R and R can be n-alkyl [CH (CH n-alkoxy [CH (CH ),,O] and acyloxy [CH (Cl-I ),,CO groups.

The cinnamic acid esters (cinnamates) which constitute the liquid crystals within the system may be prepared by the following method. First, an appropriate p-substituted benzaldehyde is condensed with malonic acid in a pyridine/piperidine medium at C. The resulting cinnamic acid is isolated and purified by recrystallization from either an acetic acid solution or an ethanol/water solution. The resulting purified acid is treated with thionyl chloride in order to form the appropriate acid chloride. The resulting acid chloride is reacted with an appropriate p-substituted phenol at a reaction temperature of 100C to yield the desired disubstituted-p,p-phenyl cinnamate which is a liquid crystal within the system.

EXAMPLE 1 Preparation of a cinnamic acid ester of the formula First, the p-substituted cinnamic acid is produced as follows. A solution of 23 grams of p-n-butylbenzaldehyde, 22 grams of malonic acid, 40 milliliters of pyriline and 10 drops of piperidine is heated at 100C for 3 hours. After this time, the mixture is passed over grams of ice and 125 milliliters of concentrated hydrochloric acid. The precipitate that forms is filtered and washed with dilute hydrochloric acid and water and recrystallized either from acetic acid or ethanol/water mixtures. The recrystallized precipitate constitutes the desired p-substituted cinnamic acid. The preparation of the liquid crystal continues as follows. A solution containing 4.3 grams of the above purified acid and 3 grams of thionyl chloride is heated over a steam bath until hydrogen chloride ceases to be evolved (about 2 hours), and is then allowed to cool. To the resulting mixture is added 3.7 grams of redistilled p-n-butyl- 3 phenol and heating is continued until the evolution of hydrogen chloride ceases. n-Hexane is then cautiously added and the resultant mixture cooled until crystals precipitate. The crystals are collected and recrystallized several times from n-hexane. The final recrystallized precipitate is the desired cinnamic acid ester.

EXAMPLE 2 Preparation of p-n-pentanoyloxycinnamic acid. 40.4g (0.3 mole) of pentanoyl chloride was slowly added to a cooled solution (about 5C) of p-hydroxycinnamic acid in 175 g of dry pyridine over a period of 30 minutes. The mixture was stirred for four hours while the temperature slowly increased to room temperature. The resulting solution was poured over ice and slowly acidified with dilute H 80 The resulting material was allowed to solidify and then filtered. This solid product was purified by Norite treatment of the first of several recrystallizations from ethanol/water.

temperatures for the transitions between crystal and smectic states; between smectic and nematic or crystal and nematic states as the case may be; and between nematic and isotropic states are given. A monotropic transition is one which occurs only while cooling the liquid crystal from its nematic state. The monotropic state occurs prior to crystallization as a solid.

Mixtures of properly selected cinnamates within this invention exhibit much greater nematic temperature ranges than the individual components. The nematic temperature ranges of these mixtures normally extend to below the melting point of any individual component. This is illustrated by the examples 3-6 below and Table II. To form such a mixture, the desired proportions of individual compounds are heated together to above the nematic-isotropic transition temperature of each component compound to form a solution which then displays a widened temperature range. The compound numbers in the following examples refer to the This procedure afforded 20 g (40%) of the desired 20 compounds as identified in Table I.

Table I Transition Temperatures for p,p'-trans-Cinnamates No. R R2 Crystal- Smectic-Nematic Nematic- Smectic or Crystal-Nema- Isotropic (C) tic if no Smec- (C) 1 c 11 c 11,, 59.7 69.6 2 can, c 11,, 52.5 61.3 3 c 14,; c 11,, 81.1 104.9 4 CH CHSO 81.3 88.8 5 CH3O C3H1 100.5 103.9 6 CH O (2.11 81.8 93.0 7 C;H,,0 C 11,, 96.2 102.0 8 c n o 1-1.. 99.1 138.8 9 C l-[ O C4H9 72.9 86.1 110.7 10 c.1-1 co 0 11.0 l08.9(88.9)* 139.3 1 1 C.l-1;,C0 C H O 94.6 140.1 12 C l-l CO CH3 87.6 120.7 13 C5HHCO, C 11 73.2 119.3 14 s ii z s n 99.1 106.6 15 c i-l co CH3O 69.3 136.6 16 c 1-1,,co c u o 95.9 147.3 17 C5HHCOZ c.11 0 101.0 150.5 18 cm co CH 94.8 112.1 19 C1H15CO2 c 11 74.6 108.4 20 c,11.,,co c 11 100.2 117.0 21 C,H,,C0 0.1-1; 70.0(43.0)* 96.2 114.0 22 C,1-1,,Co C 11,, 88.7(63.7)* 103.0 117.6 23 cm co CH3O 68.5 75.4 138.8 24 C,1-1, co (3 11 0 94.6 147.0 25 cm co c.14 0 83.1 95.1 138.8

*Monotropic transition p-n-pentanoyloxycinnamic acid in crystalline form which has a melting point of 149.5C. EXAMPLE 3 p-Tolyl-p-n-pentanoyloxycinnamate was produced A mixture composed of 43.3 mole of compound from the above p-n-pentanoyloxycinnamic acid as folnumber 6 (having a nematic temperature range of lows. 1.3g (0.01 moles) of thionyl chloride was slowly I l.2C-from 818C to 93C); 37 mole of compound added toawell stirred mixture of p-n-pentanoyloxycinnumber 4 (having a nematic temperature range of namic acid (2.6g, 0.01 mole) and 75 ml of benzene, 7.5C-from 813C to 888C) and 19.7 mole %ofcomwhile maintaining the reaction mixture of 50C. The pound number 3 (having a nematic temperature range temperature was slowly raised to reflux (about 80C) of 238C from-8l.lC to lO4.9C) has a nematic temand held there until no further evolution of gases ocperature range of 52.5C-from 40C to 925C. The curred and then cooled to 25C. About 1.1g (0.01 mixtures nematic temperature range begins 4l.lC moles) pre-cresol was added to the reaction mixture below the melting point of the lowest melting point of which was then refluxed for two hours. The solution any individual compound included in the mixture and is was cooled and the precipitate which formed was colmore than twice as wide as the widest nematic temperalected. Several recrystallizations from isopropyl alcoture range of an individual compound in this mixture. hol ave 2.5 74% of the desired roduct -tol lg g( p (p y P EXAMPLE 4 n-pentanoyloxycinnamate) which had a melting point of 948C.

The transition temperatures of some cinnamates in accordance with this invention are given in Table I. The

A mixture of 30 weight of compound number 6 (having a nematic temperature range of ll.2C-from 818C to 93C); 26 weight of compound number 4 EXAMPLE A eutectic mixture (that which has the widest nematic temperature range for that set of compounds) of 57 mole of compound 6 and 43 mole of compound 15 has a nematic temperature range of 609C from 50.1C to 111C.

EXAMPLE 6 A eutectic mixture of 75 mole of compound 2 and 25 mole of compound 18 has a nematic temperature range of 26C from 42C to 68C.

Transition temperatures for various mixtures of cinnamic acid esters within the liquid crystal system are shown in Table 11.

Table 11.

EXAMPLE 8 A sample composed of. 67 mole ofnumber 2 and 33 mole of number 13 was exposed to laboratory contaminants at a temperature of 80C for 72 hours. This exposure produced no change in the color and the nematic-isotropic transition temperature of 73.6C was unchanged.

The above results contrast markedly with the results obtained from a Schiff-base material such as a eutectic mixture of p-methoxybenzylidene-p'-n-butylaniline (MBBA) and p-ethoxybenzylidene-p'-n-butylaniline (EBBA) whose nematic-isotropic transition temperature drops from 61C to 57C after being exposed to atmospheric contaminants at room temperature for a few minutes.

Although no change occurred in the above examples, it may be possible that longer exposures can result in some degradation of the sample.

The liquid crystals of this invention are useful in electro-optic display cells of the type used in optical readout calculators, watches and other displaydevices. Their usefulness is enhanced by their stability with respect to contaminants, although the display cells must be heated when crystals with melting points above ambient temperature are used.

Nematic Temperature Ranges for Several Cinnamic Acid Esters Multicomponent Mixtures The above results are typical of beneficial results of mixing liquid crystals from the system. Other mixtures have other nematic temperature ranges and are also of interest.

The favorable environmental effects achieved by the use of liquid crystals within the system is demonstrated by Example 7.

EXAMPLE 7 What is claimed is:

l. A nematic liquid crystal,

selected from the group consisting of cinnamic acid esters of the formula wherein R1 Can be cal 12 .1, C l 12 40, C1-H2,1-+1' CO and R can be CyH2y+1, C H O and C H CO and where x and y are integers with 1 s xs 10 and l sys 10, and

said nematic liquid crystal having a melting point of less than 95C.

2. A nematic liquid crystal composition comprising a mixture of two nematic liquid crystals each selected from the group consisting of cinnamic acid esters of the formula wherein R can be C H C H O, and C,H ,CO and R can be C H C H O and C H CO where x and y are integers with lsxs llandlsxs ll.

3. A nematic liquid crystal composition comprising a mixture of a plurality of nematic liquid crystal selected from the group consisting of cinnamic acid esters of the formula i H -O .R2

wherein R can be C H C H O, and

C H CO and R can be C l-l C H O, and C H- ,CO where x and y are integers with lsxsxs l1 andls s l1.

4. The nematic liquid crystal composition recited in claim 3 wherein:

in a first liquid crystal component of said mixture R CH O and R =C H in a second liquid crystal component of said mixture R1 C4H9 and R2 in a third liquid crystal component of said mixture R C4H9 and R2 C4H9; in a fourth liquid crystal component of said mixture R C l-l and R C H and said first, second, third and fourth components of said mixture comprise about 30 weight percent, about 26 weight percent, about 28 weight percent 8 and about 16 weight percent of said mixture, respectively. 5. The nematic liquid crystal composition recited in claim 3 wherein:

in a first liquid crystal component of said mixture R,

and R2 C4H9; in a second liquid crystal component of said mixture R1 C4H9 and R2 in a third liquid crystal component of said mixture R C H and R C l-l and said first, second and third components of said mixture comprise about 43.3 weight percent, about 37 weight percent and about 19.7 weight percent of said composition, respectively. 6. The nematic liquid crystal composition recited in claim 2 wherein:

in a first liquid crystal component of said mixture R C4H9 and R2 in a second liquid crystal component of said mixture R1 C5H1|O and R2 C4H11; and said first and second components of said mixture comprise about 69 weight percent and about 31 weight percent of said mixture, respectively. 7. The nematic liquid crystal composition recited in claim 2 wherein:

in a first liquid crystal component of said mixture R C4H9 and R2 C4H9; in a second liquid crystal component of said mixture R1 C1H15CO2 and R2 and said first and second components of said mixture comprise about weight percent and about 25 weight percent of said mixture, respectively. 8. The nematic liquid crystal composition recited in claim 2 wherein:

in a first liquid crystal component of said mixture R C H and R OCH in a second liquid crystal component of said mixture R C H and R CH and said first and second components of said mixture comprise about 47 weight percent and 53 weight percent of said mixture, respectively. 9. The nematic liquid crystal composition recited in claim 2 wherein:

in a first liquid crystal component of said mixture R and R2 CqHg', in a second liquid crystal component of said mixture R C H CO and R OCT-l and said first and second components of said mixture comprise about 57 weight percent and about 43 weight percent of said mixture, respectively. 10. The nematic liquid crystal composition recited in claim 1 whereim 1 4 9; R2 C4H9; and said liquid crystal melts at about 52.lC and has a nematic temperature range of from about 521C to about 613C. 

1. A NEMATIC LIQUID CRYSTAL, SELECTED FROM THE GROUP CONSISTING OF CINNAMIC ACID ESTERS OF THE FORMULA
 2. A nematic liquid crystal composition comprising a mixture of two nematic liquid crystals each selected from the group consisting of cinnamic acid esters of the formula
 3. A NEMATIC LIQUID CRYSTAL COMPOSITION COMPRISING A MIXTURE OF PLURALITY OF NEMATIC LIQUID CRYSTAL SELECTED FROM THE GROUP CONSISTING OF CINNAMIC ACID ESTERS OF THE FORMULA
 4. The nematic liquid crystal composition recited in claim 3 wherein: in a first liquid crystal component of said mixture R1 CH3O and R2 C4H9; in a second liquid crystal component of said mixture R1 C4H9 and R2 OCH3; in a third liquid crystal component of said mixture R1 C4H9 and R2 C4H9; in a fourth liquid crystal component of said mixture R1 C4H9 and R2 C5H11; and said first, second, third and fourth components of said mixture comprise about 30 weight percent, about 26 weight percent, about 28 weight percent and about 16 weight percent of said mixture, respectively.
 5. The nematic liquid crystal composition recited in claim 3 wherein: in a first liquid crystal component of said mixture R1 CH3O and R2 C4H9; in a second liquid crystal component of said mixture R1 C4H9 and R2 OCH3; in a third liquid crystal component of said mixture R1 C4H9 and R1 C5H11; and said first, second and third components of said mixture comprise about 43.3 weight percent, about 37 weight percent and about 19.7 weight percent of said composition, respectively.
 6. The nematic liquid crystal composition recited in claim 2 wherein: in a first liquid crystal component of said mixture R1 C4H9 and R2 OCH3; in a second liquid crystal component of said mixture R1 C5H11O and R2 C4H11; and said first and second components of said mixture comprise about 69 weight percent and about 31 weight percent of said mixture, respectively.
 7. The nematic liquid crystal composition recited in claim 2 wherein: in a first liquid crystal component of said mixture R1 C4H9 and R2 C4H9; in a second liquid crystal component of said mixture R1 C7H15CO2 and R2 CH3; and said first and second components of said mixture comprise about 75 weight percent and about 25 weight percent of said mixture, respectively.
 8. The nematic liquid crystal composition recited in claim 2 wherein: in a first liquid crystal component of said mixture R1 C4H9 and R2 OCH2; in a second liquid crystal component of said mixture R1 C4H9 and R2 C4H9; and said first and second components of said mixture comprise about 47 weight percent and 53 weight percent of said mixture, respectively.
 9. The nematic liquid crystal composition recited in claim 2 wherein: in a first liquid crystal component of said mixture R1 CH3O and R2 C4H9; in a second liquid crystal component of said mixture R1 C5H11CO2 and R2 OCH3; and said first and second components of said mixture comprise about 57 weight percent and about 43 weight percent of said mixture, respectively.
 10. The nematic liquid crystal composition recited in claim 1 wherein: R1 C4H9; R2 C4H9; and said liquid crystal melts at about 52.1*C and has a nematic temperature range of from about 52.1*C to about 61.3*C. 